Method and apparatus for load identification

ABSTRACT

A load communication device and method is provided, that identifies and transmits to a PSU the load requirement to operate a load device that is powered by the PSU, by analyzing the characteristics of current applied to the load device by a given input voltage generated by the PSU. The load communication device is configured to transmit between the PSU and the load device solely over the 2 wire cable that extends between the PSU and the load device.

RELATED APPLICATION/CLAIM OF PRIORITY

The present application is related to and claims priority fromprovisional application Ser. No. 61/402,489, filed Aug. 31, 2010, andentitled “Method and Apparatus for Load Identification”, whichprovisional application is incorporated by reference herein.

INTRODUCTION

While Power Supply Units (PSU) are becoming more flexible and moreintelligent, the mobile devices that are powered up by them arediversifying a lot, having different characteristics. Each consumerdevice is coming with its own PSU, fact that makes transportationdifficult and reduces the mobility of the devices.

A universal PSU should be able to adapt its output characteristics tovaried load devices requirements. Many today's PSU are already capableof such adaptation and their flexibility will increase in the future.However, the information regarding the load device characteristics haveto be transferred from the load to the PSU. No human intervention orminimum intervention should be involved in order to facilitate theinformation transfer. The load devices have to be intelligent in orderto communicate to the PSU without human intervention. For load deviceswithout intelligence, a buffer device has to be added in order tofacilitate the load recognition by the PSU and human intervention isrequired to make the selection.

In all cases means of communication between PSU and load devices arenecessary. Radio signal and infrared beam are popular means ofcommunication; however, they are complicated and expensive.Communication through electric connection is much cheaper and reliable;therefore a supplementary electrical connection between PSU and loaddevices is necessary in order to transfer information. Usually a minimumtwo wire electrical connection is used for power transfer between PSUand load device (two-wire power cable) and this is the cheapest way ofpower transfer. Hence a third wire or more wires are necessary toestablish the information transfer by electrical connection means. Priorart describes various ways of communication by dedicated electricalconnection. The information can be transferred in analog format, digitalformat or combinations of the two.

SUMMARY OF THE PRESENT INVENTION

The object of the present patent is a method and apparatus fortransferring information between PSU and load devices by electricalmeans, without using any supplementary electrical connection but thepower wires (e.g. the 2 wire cable that extends between the PSU and theload devices). The PSU can be any of the known types: DC-DC, AC-DC,AC-AC and DC-AC.

In accordance with a basic aspect of the present invention, a loadcommunication device is provided that identifies and transmits to a PSUthe load requirement to operate a load device that is powered by thePSU, by analyzing the characteristics of current applied to the loaddevice by a given input voltage generated by the PSU.

According to a preferred embodiment, the load communication device isconfigured to transmit between the load device and the PSU solely overthe 2 wire cable that extends between the PSU and the load device. Theload communication device may include an intelligent tip (iTip) formingpart of the load, or an iTip that is physically outside the load,located between the PSU and the load and in communication with each ofthe PSU and the load over the 2 wire cable that extends between the PSUand the load device. The iTip may have a stored library of thevoltage-current-time characteristics for one or more different loadsthat are used to identify the actual load. For example, the PSU may beconfigured to deliver an initial low output voltage, voltage levelsufficient to bias an iTip in circuit communication with the PSU and theload, but far from the operation voltage level required by the loaddevice; therefore the load device is drawing no power from the PSU whilethe iTip is biased and functional. For example, 1 to 2 volts deliveredfrom the PSU are sufficient for biasing the iTip while the load deviceoperates at voltages above 3 volts.

In one version of the invention, the load communication device (iTip) isphysically outside of PSU and communicates with the PSU during the lowvoltage state of the PSU output.

In more specific aspects of the present invention, (a) communicationduring low state voltage is done by coding the data in analogue and/ordigital format, (b) the communication during low state voltage is donein different ways such as (i) coding the data in voltage, (ii) codingthe data in current, (iii) coding the data in time, and/or (iv) codingthe data in frequency. In addition, the communication during low statevoltage is effected by transferring one, two ore more loadcharacteristics. Moreover, communication during low state voltage isprotected by a switch against the back bias voltage of the battery ofthe load. Still further, communication during low state voltage is doneby means of a high frequency filtered path while the power transferbetween PSU and load is done means of low frequency filtered path usingthe same 2-wire cable.

In another embodiment of the present invention, the load communicationdevice (iTip) is physically outside of PSU and communicates with the PSUduring the high voltage state of the PSU output by clamping the maximumoutput voltage of the PSU.

Additional features of the present invention will be apparent from thefollowing detailed description and the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a classical connection between aPSU and load devices using two-wire power cable;

FIG. 2 schematically illustrates the connection between an intelligentPSU and intelligent load device using a two-wire power cable, where theinformation transfer is facilitated by an intelligent port present inthe load device, according to the principles of the present invention;

FIGS. 2A, 2B and 2C schematically illustrate how the PSU can identifythe type of load and the voltage required to power that type of load,according to the principles of the present invention;

FIG. 3 schematically illustrates the connection between intelligent PSUand a classical load device, where an intelligent buffer device(intelligent tip or “iTip”) is added on the power wires path, inaccordance with the principles of the present invention;

FIG. 4 schematically illustrates the PSU voltage and current when onlyone characteristic is transferred under the form of current pulse width,in a device or method according to the present invention;

FIG. 5 schematically illustrates an example of the circuitry thatproduces iTip function, in a device and/or method according to thepresent invention;

FIG. 6 is a schematic example of an implementation of the time encodingmethod of the present invention; where a delay was inserted between themoment T1 and the moment the iTip is applying a load current;

FIG. 7 schematically illustrates the PSU voltage and current when iTipis transferring data encoded into load current frequency, in accordancewith the present invention;

FIG. 8 schematically illustrates the PSU voltage and current when iTipis transferring one characteristic information base on the amplitude ofthe load current ISET.

FIG. 9 schematically illustrates circuitry for producing the currentamplitude encoding method, according to the principles of the presentinvention;

FIG. 10 schematically presents the PSU voltage and current when iTip istransferring one or more characteristics information base on the voltageamplitude set by iTip while PSU is set at a low power limit;

FIG. 11 schematically presents the PSU voltage and current when iTip istransferring one or more characteristics information base on a digitalcode pattern;

FIG. 12 schematically presents the PSU voltage and current when iTip istransferring one characteristic information base on the maximum voltageamplitude set by iTip;

FIG. 13 shows a circuit implementation of an electronic switch (M1) forcircuitry shown in FIG. 9 (current amplitude encoding).

FIG. 14 schematically illustrates how PSU output rises to the desiredtarget, in accordance with the principles of the present invention(using the circuitry of FIG. 13);

FIG. 15 schematically illustrates an example of high frequencycommunication between iTip and PSU independent of the DC voltage levelpresent on the 2-wire cable, in accordance with the principles of thepresent invention

FIG. 16 is a schematic illustration of an intelligent PSU that may beused for information transfer, in a system and method according to theprinciples of the present invention.

DETAILED DESCRIPTION

As described above, the present invention relates to a method andapparatus of information transfer between load devices and PSU byelectrical means, without using any supplementary electrical connectionbut the power wires (e.g. the 2 wire cable that extends between the PSUand the load devices). The PSU can be any of the known types: DC-DC,AC-DC, AC-AC and DC-AC, and in accordance with a basic aspect of thepresent invention, a load communication device is provided thatidentifies and transmits to a PSU the load requirement to operate a loaddevice that is powered by the PSU, by analyzing the characteristics ofcurrent applied to the load device by a given input voltage generated bythe PSU. The principles of the present invention are described herein inconnection with several examples, and from that description, the mannerin which the present invention can be practiced will be apparent tothose in the art.

In this application, reference to a “load communication device” isintended to encompass an “intelligent” tip (iTip) forming part of theload (e.g. as shown in FIG. 2), or an iTip that is physically outsidethe load, located between the PSU and the load and in communication witheach of the PSU and the load over the 2 wire cable that extends betweenthe PSU and the load device (e.g. as shown in FIG. 3). Also, referenceto a device being “intelligent” or “smart” is intended to mean that thedevice has circuitry analogue or digital capable of generating andor/receiving data encoded in the manner described in this application

Initially, FIG. 1 is a schematic illustration of a classical connectionbetween a PSU 100 and a load device 102 using a two-wire power cable103.

FIG. 2 schematically illustrates the connection between an intelligentPSU 104 and intelligent load device 106 using a two-wire power cable103, where the information transfer is facilitated by an intelligentport, or iTip, 108 present in the load device 106, according to theprinciples of the present invention.

FIGS. 2A, 2B and 2C schematically illustrate an example of how the PSU104 can identify the type of load and the voltage required to power thattype of load, according to the principles of the present invention. Thegoal is for the PSU 104 to be able to identify the type of load and thevoltage required to power that type of load. For different loads, thereare discrete voltage levels, which are suitable to power it. As oftoday, these voltages are 5V, 8.4V, 10V, 12V, 16V and 19.5V. These arethe voltage levels, which can power up most of the portable devices onthe market today. That may change in the future but the general conceptsdescribed herein would apply to such voltage levels. One embodiment ofthis invention comprises applying step by step all the standard voltagesfor a defined period of time, while analyzing the current going to theload 106. The characteristic of the current going to the load for agiven input voltage will vary function of the type of load, though byanalyzing the characteristic of the current it can be identified if theapplied voltage is the suitable voltage for that type of load. Asuitable voltage level is the one, which is specified by themanufacturer for a proper operation of the load.

FIG. 2B depicts such concept. In this case, we do apply three voltagelevels trying to identify which voltage level is the one suitable forthe load. In this particular example, the voltage levels applied are10V, 16V and 19V. As is presented in FIG. 2A the current going to theload has a very low level until the applied voltage is 19V. By measuringthe current level for each voltage level applied, we can identify thetype of load. This is a very simple approach, which may not work in allcases. Thus, FIG. 2B illustrates a case wherein the previous algorithmmay not work. As can be seen the current level for the 16V applied tothe load is high and the suitable voltage for that load is 19V.Analyzing the current shape when the 16V it is applied is visible thatthe pattern includes current spikes, which do occur quite periodically.When the suitable voltage is applied the current level is lower and intrain of pulses. This is because the load in this case a computer wasoff. When this particular load is on the current is depicted in FIG. 2C.As shown in FIG. 2C, when the 16V voltage is applied which is notsuitable for the load we do have the pattern of current spikes but notas repetitive as in FIG. 2B.

In these particular examples, we can conclude that by applyingsuccessfully different voltage levels, which are standardized fordifferent types of load, and monitoring the current going to the load wecan identify behaviors patterns, which can be utilized in identifyingthe suitable voltage. When more type of loads are introduced on themarket, we may face the situation wherein the algorithm in identifyingthe suitable type of load has to be updated. This is due to the newdesign concept for the power supply inside of the load, which works as abuffer between the source and the electronics inside of the load. Inconclusion, by applying successively the standard voltage levels with azero voltage reset in between and a period of time long enough toaddress the transient behavior of the load current, we can identifyclear patterns of the load current which can be utilized in identifyingthe suitable voltage level for that particular load.

FIG. 3 presents the connection between intelligent PSU 104 and aclassical load device e.g. the type of load device shown at 102 in FIG.1, where an intelligent buffer device (intelligent tip or “iTip”) 110 isadded on the power wires 103 path. This intelligent tip stores theinformation regarding the load characteristics and the means tocommunicate with the PSU. For the purpose of this patent presentation,the functions of the intelligent port (iTip 110) and the intelligent tipiTip 108 in FIG. 2) are similar.

The intelligent port/tip (iTip) can be biased (powered up) by the PSU,by the load device itself or by an external power source. For thefollowing presentation the iTip is considered to be biased by the PSU.

For simplicity of the presentation, the PSU shown in FIGS. 1, 2 and 3has DC output voltage and the load devices are operating with DC inputpower.

Intelligent Load Recognition

The intelligent PSU (e.g. PSU 104) is configured to deliver an initiallow output voltage, voltage level sufficient to bias the iTip but farfrom the operation voltage level required by the load device; thereforethe load devices is drawing no power from the PSU while the iTip isbiased and functional. This assumption is met in majority of theapplications; 1 to 2 volts are sufficient for biasing the iTip while theload device operates at voltages above 3 volts.

Because the load device is not operating at the low voltage necessary tobias the iTip, the communication between the PSU and the iTip is notinterfered by the presence of the load device; at the same time, theload device is in a safe state, as its input voltage is under itsfunctional range.

The data is transferred from the iTip to PSU during this low voltagestate. After the data is received the iTip is turned off and the PSU isramping up its output to the desired level. During the normal operationof the load device the iTip is disabled and it is not interfering withthe load device operation. The power consumption of the iTip isnegligible (very small) during the load device operation.

The information transfer can be done by coding the data in voltage,current, time (pulse with, duty cycle) and frequency. Each of this dataencoding modes can be used alone or in combination with the others. Theformat of information can be analog or digital.

The data communicated can comprise one minimal characteristic load(example: output voltage), two characteristics (example: output voltageand current) or more characteristics (example: output voltage, outputcurrent, over-voltage protection level, under-voltage protection level,over-temperature protection level, power surge level etc.).

Time Encoding

FIG. 4 schematically illustrates the PSU voltage and current when onlyone characteristic is transferred under the form of current pulse width.The PSU is using the sensing of its output current as means ofcommunication. As shown in FIG. 4, during time interval T0-T1, the PSUis increasing its output voltage from zero to 2 volts; during timeinterval T1-T2 the IPT is applying a specific current load Iset whilePSU maintains its output constant and it is measuring the time interval.At the moment T2 the IPT is reducing its load current to zero and PSU isfinishing counting. During time interval T2-T3 the PSU is processing thetransferred data into target output voltage based on a preset algorithm.During time interval T3-T4 the PSU is ramping up its output to thetarget voltage. After T4 the output voltage of PSU is maintained at itstarget value and the load device can operate properly.

FIG. 5 presents one possible implementation of the circuitry thatproduces iTip function, in accordance with the principles of the presentinvention. In the circuitry of FIGS. 5, J1 and J2 are the ITIPconnections to the negative power wire (GND) and J3 and J4 are the ITIPconnections to the positive power wire (Vout). Once the bias voltage isapplied by the PSU, a positive reference voltage dictated by R4 and R5resistive divider is applied to the non-inverting input of Operationalamplifier U1, while the inverting input of U1 is held low to groundbecause C1 capacitor is initially discharged. U1 output state becomeshigh, turning on M1 mosfet transistor. The current flows from Vout toGND through R1, R2 and M1; therefore a load current is applied to PSUoutput. This condition last until C1 is charged up to the same potentialas the one set as reference by the R4 and R5. Once the C1 voltageexceeds the reference voltage, U1 output switch to GND; therefore it isturning off M1 and terminates the flow of current from PSU output. Thecharging time of C1 is set by R6 resistor. The time of current flowingis set by choosing C1 and R6 values.

A second implementation of the time encoding method is schematicallypresented in FIG. 6, where a delay was inserted between the moment T1and the moment the IPT is applying a load current. The duration of thisdelay is itself characteristic information. Therefore two characteristicdata can be communicated from ITIP to PSU, one encoded into the T1-T2delay, the second encoded into T2-T3 load current duration.

Frequency Encoding

FIG. 7 schematically presents the PSU voltage and current when IPT istransferring data encoded into load current frequency. The duty-cycle ofthe iTip current can be used to communicate a second characteristic ofthe load device.

Current Amplitude Encoding

FIG. 8 schematically presents the PSU voltage and current when iTip istransferring one characteristic information base on the amplitude of theload current ISET. Once PSU receive the data and its ramping up itsoutput voltage the iTip is self-turning off (T3-T4). After T5 the outputvoltage reaches the target level and the load device can operate.

FIG. 9 schematically illustrates circuitry for producing the currentamplitude encoding concept, according to the principles of the presentinvention. As shown in FIG. 9, once the bias voltage is applied fromPSU, transistor Q2 is turn on by the current injected in its based byR4. The Q2 collector current is polarizing the base-emitter junction ofQ1, therefore Q1 is on in a saturated state. Its collector current islimited by resistor R1. Hence the current amplitude sink from PSU iscontrolled by R1. As long as the PSU voltage maintains the low biasvoltage Q3 is off, because R2 and R3 are chosen to deliver a basevoltage lower than the activation level. After the PSU has received theinformation encoded in the IPT current, its voltage is rising in orderto reach the target demanded for the load device (after T2). At T3 thePSU voltage has increased enough for the base voltage of Q3 to becomeactive. As PSU output voltage continues to increase, Q3 becomes moreactive, its collector current reducing he base current of Q2,consequently reducing the collector current of Q1 (T3-T4). At the momentT4 the current through Q1 becomes zero; the only remaining currentflowing through IPT is that of Q3, which is negligible.

Voltage Clamping Encoding

FIG. 10 schematically presents the PSU voltage and current when iTip istransferring one characteristic information base on the voltageamplitude set by iTip. A limited power capability from PSU is activatedin order to help with the output voltage clamping. The clamping voltagelevel VSET is decoded by PSU as a target characteristic. At T2 theclamping is terminated by the iTip and PSU is raising the output voltageto the target level. The duration of the clamping can be use as a secondcharacteristic information as described in the section above subtitled“Time encoding”.

FIG. 11 schematically presents the PSU voltage and current when IPT istransferring one or more characteristics information base on a digitalcode pattern. As shown in FIG. 11, during T2-T3 interval, the iTipgenerates a modulated load current based on a digital code. The iTip mayincorporated a microcontroller or/and a memory IC in order to producesuch a digital data transfer.

Prior art (U.S. patent application Ser. No. 12/772,165) proposes adigital communication between PSU and an intelligent load by means of adedicated third wire and classical digital voltage signal. Thecommunication is bidirectional and continues during the operation of theload device. In the present method the digital communication is reusingthe power wires, is preferably unidirectional, and takes place only whenthe load device is inactive and it is achieved through current signal.

Thus, as seen from the foregoing description, the present inventionprovides a load communication device that identifies and transmits to aPSU the load requirement to operate a load device that is powered by thePSU, by analyzing the characteristics of current applied to the loaddevice by a given input voltage generated by the PSU. The loadcommunication device is configured to transmit between the PSU and theload device solely over the 2 wire cable that extends between the PSUand the load device.

Additional features of the invention are described herein.

Maximum Voltage Clamping Encoding

There are some load devices on today's consumer market that have theinternal battery exposed to in input; therefore a significant voltagelevel is presented all the time on the input port. In such cases the lowvoltage generated by the power supply in order to communicate with theiTip is overwritten by the back bias voltage from the internal battery.The communication between iTip and the power supply cannot have placebased on the method described previously (e.g. in the sectionsidentified above as “Time encoding”, “Frequency encoding”, “Currentamplitude encoding” and “Voltage clamping encoding”). FIG. 12 presentsthe PSU voltage and current when iTip is transferring one characteristicinformation base on the maximum voltage amplitude set by iTip. As shownin that figure, the clamping voltage level VSET is decoded by PSU as atarget characteristic. VSET is in this case set slightly above thenominal output voltage (but still in the working input range of theload), therefore any voltage leaking from the internal battery do notaffect the communication. At T1 the PSU voltage exceeds the desirednominal output voltage and at T2 it reaches the clamping VSET level whenthe iTip is raising its current, clamping the PSU output voltage (powerlimit). The clamping voltage level of iTip communicate to the PSU thedesired output voltage and PSU output goes there, exiting the clampingrange of the iTip at T3. the iTip current goes to zero at T3 and the PSUis working at the desired output voltage.

Output Voltage Back-Bias Protection

In case of back bias from the battery of the load the communicationbetween iTip and the power supply cannot have place based on the methoddescribed previously (e.g. in the sections identified above as “Timeencoding”, “Frequency encoding”, “Current amplitude encoding” and“Voltage clamping encoding”). One way the overcome this issue is the adinside of iTip an back-bias blocking switch. FIG. 13 shows animplementation of such electronic switch (M1) for circuitry shown inFIG. 9 (current amplitude encoding). In FIG. 13, M1 mosfet is normallyOFF, disconnecting PSU output from the load (inside of iTip). Any backbias voltage from the battery of the load does not interfere with theiTip. M1 is controlled by transistor Q4, which is off for the low biasvoltage applied by PSU. The current amplitude circuit of iTip works asdescribed in the foregoing section entitled “Current amplitudeencoding”. Once the bias voltage is applied from PSU, transistor Q2 isturn on by the current injected in its based by R4. The Q2 collectorcurrent is polarizing the base-emitter junction of Q1, therefore Q1 ison in a saturated state. Its collector current is limited by resistorR1. Hence the current amplitude sink from PSU is controlled by R1. Aslong as the PSU voltage maintains the low bias voltage Q3 is off,because R2 and R3 are chosen to deliver a base voltage lower than theactivation level. After the PSU has received the information encoded inthe (current amplitude encoding) current, its voltage is rising in orderto reach the target demanded for the load device (after T2). At T3 thePSU voltage has increased enough for the base voltage of Q3 to becomeactive. As PSU output voltage continues to increase, Q3 becomes moreactive, its collector current reducing he base current of Q2,consequently reducing the collector current of Q1 (T3-T4). At the momentT4 the current through Q1 becomes zero; the only remaining currentflowing through IPT is that of Q3, which is negligible.

The PSU output rises to the desired target, process during which the Q4is activated based on R6 and R7 resistor divider, when output voltageexceeds VON. Once Q4 saturates the gate of M1 is pulled down and M1 isactivated, connecting the output of PSU to the load (T5), asschematically shown in FIG. 14.

High Frequency Filtered Communication

FIG. 15 schematically presents the high frequency communication betweeniTip (by means of analogue or digital encoding) and PSU independent ofthe DC voltage level present on the 2-wire cable. The iTip includes ahigh frequency reject filter at the load end while the PSU has a similarfilter at its output. L1 and L2 are low frequency pass filters thatallow only the DC power current to circulate between the PSU and load.C1 and C2 are high frequency filters that allow only the communicationsignal to pass between encoder circuit of the iTip and the decodercircuit of the PSU. The encoder and decoder are biased from the 2-wirepower connection and are processing high frequency low power signal,using analogue or digital signal. The PSU output voltage is low comparedto the load operation voltage and no power is drawn by the load. Thecommunication is not compromised when the load presents a back biasvoltage from the battery of the load. After the PSU acquires the targetoutput voltage from the iTip, the output voltage of PSU rises to thedesired voltage level and power transfer to the load can commence, whilethe communication from the iTip can be terminated.

Further Comment

FIG. 16 is a schematic illustration of an intelligent PSU that may beused for information transfer, in a system and method according to theprinciples of the present invention. Specifically, FIG. 16 is aschematic illustration of a PSU that may have a degree of intelligence,in the sense that it would be capable of identifying a load based on astored load library (in its microcontroller). Such a PSU could be usedin the system shown in FIG. 2, because it would still operate on thesame 2 wire cable that transmits the power between the PSU and load. Theload communication device would still comprise the iTip (e.g. the iTipforming the load port in the example of FIG. 2), so that each of theload and the PSU would have “smart” circuitry capable of communication.

SUMMARY

The foregoing description shows how the principles of the presentinvention can be implemented to provide for transferring informationbetween PSU and load devices by electrical means, without using anysupplementary electrical connection but the power wires (e.g. the 2 wirecable that extends between the PSU and the load devices). With theforegoing description in mind, the manner in which the principles of thepresent invention can be implemented for various types of PSU and loaddevices will be apparent to those in the art.

1. Apparatus comprising a load communication device that identifies andtransmits to a PSU the load requirement to operate a load device that ispowered by the PSU, by analyzing the characteristics of current appliedto the load device by a given input voltage generated by the PSU.
 2. Theapparatus of claim 1, wherein the load communication device isconfigured to transmit between the PSU and the load device solely over a2 wire cable that extends between the PSU and the load device.
 3. Theapparatus of claim 2, where the load communication device has a storedlibrary of the voltage-current-time characteristics for different loadsthat is used to identify the actual load.
 4. The apparatus of claim 2,where the load communication device is physically outside of PSU andcommunicates with the PSU during the low voltage state of the PSUoutput.
 5. The apparatus of claim 2, where the load communication deviceis in circuit communication with the PSU during low state voltage and isconfigured to transfer one, or a plurality of load characteristics. 6.The apparatus of claim 2, where the device is physically outside of PSUand communicates with the PSU during the high voltage state of the PSUoutput by clamping the maximum output voltage of the PSU.
 7. Theapparatus of claim 2 where the where the load communication device is incircuit communication with the PSU during low state voltage and thecommunication during low state voltage is protected by an switch againstthe back bias voltage of the battery of the load.
 8. The apparatus ofclaim 2, where the where the load communication device is in circuitcommunication with the PSU during low state voltage and thecommunication during low state voltage is done by means of highfrequency filtered path while the power transfer between PSU and load isdone means of low frequency filtered path using the same 2-wire cable.9. The apparatus of claim 1, where the load communication device has astored library of the voltage-current-time characteristics for differentloads that are used to identify the actual load.
 10. The apparatus ofclaim 1, where the load communication device is physically outside ofPSU and communicates with the PSU during the low voltage state of thePSU output.
 11. The apparatus of claim 1 where the load communicationdevice is in circuit communication with the PSU during low state voltageby coding the data in analogue and/or digital format.
 12. The apparatusof claim 1 where the load communication device is in circuitcommunication with the PSU during low state voltage in any or all ofvoltage, current, time and frequency.
 13. The apparatus of claim 1,where the load communication device is physically outside of PSU andcommunicates with the PSU during the high voltage state of the PSUoutput by clamping the maximum output voltage of the PSU.
 14. A methodfor identifying and transmitting to a PSU the load requirement tooperate a load device that is powered by the PSU, comprising a.providing communication between a load communication device and a PSUthat analyzes the characteristics of current applied to the load deviceby a given input voltage generated by the PSU, and b. transmitting tothe PSU the load requirement to operate a load device that is powered bythe PSU.
 15. The method of claim 14, wherein the load communicationdevice transmits between the PSU and the load device solely over a 2wire cable that extends between the PSU and the load device.
 16. Themethod of claim 15, where the load communication device has a storedlibrary of the voltage-current-time characteristics for different loadsthat is used to identify the actual load.
 17. The method of claim 15,where the load communication device is physically outside of PSU andcommunicates with the PSU during the low voltage state of the PSUoutput.
 18. The method of claim 15, where the load communication deviceis in circuit communication with the PSU during low state voltage andtransfers one, or a plurality of, load characteristics.
 19. The methodof claim 15, where the load communication device is physically outsideof PSU and communicates with the PSU during the high voltage state ofthe PSU output by clamping the maximum output voltage of the PSU. 20.The method of claim 15, where the where the load communication device isin circuit communication with the PSU during low state voltage and thecommunication during low state voltage is protected by an switch againstthe back bias voltage of the battery of the load.
 21. The method ofclaim 15, where the where the load communication device is in circuitcommunication with the PSU during low state voltage and thecommunication during low state voltage is done by means of highfrequency filtered path while the power transfer between PSU and load isdone means of low frequency filtered path using the same 2-wire cable.